The present invention relates generally to a control system for controlling the air fuel ratio of an internal combustion of an automotive vehicle, and more particularly, to a method and apparatus for controlling a fuel pulse width in response to changes in a normalized air charge and in a normalized purge vapor flow from an engine fueling system.
Minimizing tailpipe emission is an objective of closed loop fuel systems. Closed loop fuel systems include a catalytic converter that is used to treat the exhaust gas of an engine. The efficiency of a catalytic converter is affected by the ratio of air to fuel supplied to the engine. At the stoichiometric ratio, catalytic conversion efficiency is high for both oxidation and reduction conversions. The air/fuel stoichiometric ratio is defined as the ratio of air to fuel which in perfect combustion would yield complete consumption of the fuel. The air/fuel ratio Lambda of an air/fuel mixture is the ratio of the amount by weight of air divided by the amount by weight of fuel to the air/fuel stoichiometric ratio. Closed loop fuel control systems are known for use in keeping the air/fuel ratio in a narrow range about the stoichiometric ratio, known as a conversion window.
The difficulty with known systems is that the catalyst is very sensitive to errors in the input air fuel mixture. Fueling errors may result in catalyst breakthrough and therefore a reduction in the efficiency of the catalyst.
Known engine air-fuel control systems generally execute control steps using several stored conversion/determination tables to control delivery of an air-fuel mixture to an engine cylinder. For example, known systems generally perform the following steps: (i)measure a signal generated by an mass air-flow sensor; (ii)determine a measured air flow value using an air flow table indexed by a voltage of the mass air flow sensor signal; (iii)determine an air charge per cylinder using an air charge table indexed by the measured air flow and the speed (RPM) of the engine; (iv)determine a fuel charge based on fuel table indexed by air charge per cylinder; (v)calculate a fuel injector pulse width based on the fuel charge.
As discussed, the known engine control systems utilize the air flow table, the air charge table, and the fuel table for engine air-fuel control. The development of these tables during engine calibration at a vehicle design center involves considerable time and effort. Further, the numerous tables require a relatively large amount of memory in the engine controllers which leads to increased engine cost.
The present invention provides a method and apparatus for controlling the operation of an engine of the automotive vehicle by determining an overall fuel pulse width that is a function of air charge load and the purge function.
In one aspect of the invention, a method for controlling an amount of fuel delivered to a cylinder of an internal combustion engine includes determining a first amount of fuel to deliver to said cylinder based on a current air charge of said cylinder and a desired air-fuel ratio, calculating a first air-fuel ratio change value based on an amount of change in the air charge, calculating a second air-fuel ratio change value based on an amount of change in purge flow to the cylinder, and delivering a second amount of fuel to the cylinder based on the first amount of fuel, and the first and second air-fuel ratio change values.
In a further aspect of the invention, a control system for controlling an engine of an automotive vehicle has an air charge sensor generating a first signal indicative of an air charge, a purge flow valve generating a second signal indicative of purge flow. A controller is coupled to the air charge sensor and the purge flow valve. The controller is configured to determine a first amount of fuel to deliver to the cylinder based on the first signal and a desired air-fuel ratio. The controller is configured to calculate a first air-fuel ratio change value based on the first signal and is configured to calculate a second air-fuel ratio change value based on the second signal. The controller is configured to deliver a second amount of fuel to the cylinder based on the first amount of fuel and the first and second air-fuel ratio change values.
The inventors herein have recognized that engine air-fuel control systems can be greatly simplified by (i) determining an initial fueling amount upon engine startup and (ii) adjusting the fueling amount based on xe2x80x9cchangesxe2x80x9d in engine load and vapor purge. By simply adjusting the fuel amount based on subsequent changes in engine load and vapor purge, the inventive control strategy eliminates the air charge table and the fuel table, required by known systems. Thus, the inventive control system results in considerable timing savings during vehicle calibration (since the air charge table and the fuel table need not be developed) for a given engine. Further, by eliminating the two tables, the memory size of the engine controller can be reduced resulting in engine cost savings. Further, one skilled in the art will recognize that the method is much simpler to implement than known methods.